If an optical disc as an information signal recording medium has foreign matter such as dust, fingerprint or the like adherent to the signal recording surface thereof, for example, information signal may not possibly be recorded or reproduced accurately. On this account, the optical disc of this type is usually encased in a cartridge body for use as a disc cartridge. For example, the optical disc is rotatably encased in a cartridge body having a write/read opening. The cartridge body has provided therein shutter members to cover and uncover the write/read opening. The disc cartridge provided with the shutter members has the opening covered with the shutter members when it is not used in a recorder and/or player, to protect the optical disc held in the cartridge body. When the disc cartridge is loaded in the recorder and/or player, the shutter members are moved by a shutter releasing mechanism provided in the recorder and/or player to uncover the write/read opening.
In the meantime, the optical discs include a one adopting a recording format in common to an optical disc pre-encased in a disc cartridge and which can be loaded, being bare, namely, not being encased in any cartridge, in a dedicated recorder and/or player to under go write or read of information signal.
However, in case one of the optical discs is loaded, encased in a disc cartridge, into a recorder and/or player while the other is loaded, not encased in any cartridge, into a recorder and/player, information signal cannot be written to, or read from, these two optical discs by any common recorder and/or player even if the optical discs adopt a recording format in common.